A Central Intelligence Agency official testified yesterday that a key witness in the trial of two men charged with espionage demanded more money and benefits before she agreed to cooperate with government investigators.

Robert D. Hall, a CIA "case officer," repeatedly contradicted the earlier testimony of Dung Krall, a CIA-paid double-agent. Prosecutors allege she was the courier for secret State Department cables that two men sent to Vietnamese diplomats.

Hall, appearing as a defense witness, claimed that Krall had demanded a $45,000 bonus from the CIA when her services as an undercover agent ended, that she refused to take a London assignment unless given a $1,200 bonus, and that she inisisted on other benefits before agreeing to testify in the case. Krall had said she made none of the demands.

Hall was called to testify by attorneys for David Truong, a Vietnamese expatriate charges, along with former United States Information Agency employe Ronald L. Humphrey, with passing the diplomatic documents to Vietnamese officials in Paris.

Humphrey is charged with taking the documents from the USIA where he worked in giving them to Truong. Truong is accused of giving them to Krall with instructins to deliver them to the Communist officials.

Hall was Truong's first witness in the Vietnamese espionage case, which ended its eighth day yesterday in U.S. District Court in Alexandria. Hall's testimony was aimed at discrediting Krall's testimony which is central to the government case.

Truong's attorneys have contended that Krall would "entrap and ensnare others" for money.

Humphrey testified Monday that he gave confidential classified State Department documents to Truong, who sometimes lobbied for Vietnamese causes on Capitol Hill, out of his desperate love for his Vietnamese common-law wife, Kim, and her five children, who were trapped by the Communists in Vietnam.

Humphrey destified that he had hoped the information would help improve relations between Vietnam and the U.S. and that, in some indirect way, speed the release of Kim and the children.

In their continuing efforts to chip away at the prosecution's case, defense attorneys presented testimony yesterday of a USIA employe who called Humphrey "enthusiastic" "though" and "very trusting." A high-ranking State Department official and a legisltaive assistant to Sen. George McGovern (D-S.D.) testified that Humphrey advised them of his efforts to release his family from Vietnam.

Humphrey's attorneys rested their case yesterday morning.

Hall said, in response to questioning, that Krall had made several demands. During one meeting her eyes filled with tears and she gripped a chair until her knuckles turned white, saying she wouldn't continue in her assignments unless she was paid more money, Hall said.

Hall also testified that the CIA paid $250 a month in rent for Krall's sister's apartment. The apartment, Hall said, was used as an "accommodation address" or a place of safety for Krall.

Hall said that at one time Krall demanded two or three years' pay, about $45,000 as a bonus when her service with the CIA ended. Hall said Krall told the FBI that he (Hall) had promised she would get the bonus. But he said yesterday he never made such a promise and that "she made rumblings about it."

Hall also testified that as a double agent Krall's mission was to investigate "certain members of the (Vietnamese) diplomatic delegation" during negotiations last year in Paris between the U.S. and Vietnam. "Whatever information she could get from the talks was part of that (her assignment) too," Hallsaid.

Morton H. Halperin, an aide to former secretary of state Henry Kissinger and former member of the National Security Council, also testified for the defense. He said that the cables Humphrey and Truong are accused of funneling to the Communists have "no information in any of them which, if given to the government of and no information in any of them whcch, if given to the government of Vietnam, could injure the United States or be advantageous to the Vietnamese."